1. Field of the Invention
The present invention concerns a device that transforms a digital signal into an acoustic signal, making use of a standard phase modulation, and having the purpose of transmitting data through a fix or mobile/cellular telephone line.
2. Description of the Related Art
It is well known that, at present, the transmission of data through acoustic coupling, performed e.g. with a common telephone, has become a quite simple operation, in particular when a standard record is used. However, the known art sets unavoidable limits for making use of said system the reliance whereof remains in any case low. The limits derive from two critical points the technique has not yet been able to overcome:                the need of a perfect alignment between transmitter and receiver (telephone). In fact, when said alignment is not perfect, the data transmission shows a high percentage of error, as it also happens when the two surfaces are not in perfect contact one with the other.        high sensibility to acoustic noise (surrounding) and to vibrations. During transmission it is necessary to remain silent and reduce (or eliminate wherever possible) the surrounding noise because it may alter the acoustic signal to be transmitted.        
The need derives from above described situation to adopt special precautions for reducing above mentioned inconveniences to the minimum, whereby they can never be completely eliminated. Some of the devices used for said purpose are listed herein below:    a. rubber bands, or similar accessories, for fixing the transmitter and the receiver so as to assure a better mechanical coupling. In particular, the transmitted must be coupled with the microphone of the telephone receiver, for receiving and consequently transmitting on the telephone line.    b. gaskets, adapters, supports etc. for assuring the sealing between the transmitter and the telephone, in consideration of the great variety of possible shapes of the latter. In fact, some “particular” telephone shapes (especially of the microphone) may even make the coupling impossible. Just think of a telephone with a modem design in which the receiver has a design in the shape of a point, like a pyramid.    c. the so-called acoustic cloth puts between the transmitter and the telephone so as to attenuate the vibrations between the two “machine bodies”, which are a sure source of transmission errors.
As far as the kind of modulation used, there exist different modulation techniques, which are characterized in the modulation records used, in error probabilities and transmission speed. There are, e.g., two kinds of modulation used also for the transmission of data through the telephone line:                frequency modulation (FSK)        phase modulation (PSK).        
The frequency modulation (FSK) is the one mostly used for transmitting data through an acoustic coupling; it shows the advantage of not being owner and to be able to use a common standard modem; on the other side, it has a low efficiency in terms of relationship signal/noise at equal transmission speed towards other modulation techniques.
The phase modulation (PSK) is a rather efficient modulation technique which allows, in theory, the data transmission at extremely high speed or, if used at a relatively low speed, with an extremely high efficiency. Due to this latter feature, it is widely used for low speed cable transmissions, where a great safety in the data transmission is required (e.g. counters for automatic drawing). Today, the phase modulation is used for the data transmission without cable only in a few cases in which a special owner record has been developed for the acoustic coupling. This implies the disadvantage that, for receiving, a non standard modem must be used that needs, for entering the net, a special approval for the telephone lines o each single Country and this is a limit that slows down the commercial development thereof. Even in the case of an acoustic coupling realized with a phase modulation and a non standard modem, the present art has not been able to solve the above mentioned inconveniences (the need of a perfect alignment between microphone and transducer and the high surrounding noise sensibility).